This invention relates generally to apparatus for sampling and characterizing aerosols. An aerosol is a colloidal system in which a gas, frequently air, is the continuous medium, and particles of solids or liquids are dispersed in it. Aerosols are commonly studied in connection with air pollution control and environmental safety. There are numerous industrial applications requiring aerosol sampling and characterization. In a nuclear reactor, for example, failure of a water-cooled fuel pin would produce fission-product aerosols under conditions of high pressure (0.35-17.5 MPa) and temperatures (700-1900 K) in the presence of steam, hydrogen, noble-gases and fission-product vapors travelling at relatively low velocities (0.1-30 cm/s). Such aerosols (in both liquid and solid states) would include particles in the 0.01-100 .mu.m range, number densities of 10.sup.3 -10.sup.8 particles/cm.sup.3, and mass loadings up to approximately 1 g/s.
The basic methods of aerosol sampling (by particle separation) are represented by four classes of instruments: impactors, impingers, centrifugal units, and gravitational units. Commercially available devices generally fall into one of these categories using only a single collection scheme. The relative efficiency of the device depends primarily on the size of particles present and the velocity of the air stream. Each collection scheme is primarily directed to a particular range of conditions. For example, impaction is effective for particles greater than one micron, whereas diffusion is effective for particles approximately 0.1 micron and below. Inertial and centrifugal samplers may have a high power demand. High efficiency in such devices is generally associated with a marked pressure drop, requiring increased power to move the air through the sampler. Gravitational units require low velocities because the number of particles removed increases with falling speed.
Therefore, it is an object of the present invention to provide an apparatus for sampling and characterizing aerosols over a wide particle size range.
It is another object of the present invention to provide an apparatus for sampling aerosols at relatively low velocities.
It is also an object of the present invention to provide an apparatus for sampling and characterizing fission-product aerosols.
Additional objects, advantages, and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention.